ABSTRACT Sepsis induces a metabolic stress on multiple systems in the body. Despite the well-recognized importance of supporting organ and tissue metabolism in sepsis with appropriate nutrition, current nutritional approaches are generally unsuccessful at preventing muscle loss and gut atrophy. We propose to quantify the response of protein synthesis in the muscle, gut, and liver to specific formulations of amino acids designed to stimulate protein synthesis. Our overriding hypothesis is that there is a unique formulation based primarily on essential amino acids (EAAs) that will maximally stimulate protein synthesis in muscle and gut mucosa, while maintaining protein synthesis in the liver. In order to address our general hypothesis we will address the following specific aims: Specific Aim 1: To test the hypothesis that sepsis in pigs induces a net breakdown of muscle and gut mucosal protein; a reduced production of arginine in the gut; and a stimulation of liver acute phase proteins (represented by fibrinogen) and albumin synthesis. Specific Aim 2: To test a series of hypotheses related to the responses to specific formulations of amino acids. Those formulations are: a balanced mixture of EAAs and non-EAAs in the profile found in pig protein; a mixture of only EAAs; and, a mixture of EAAs plus 12.5% citrulline. Specific Aim 3: To test the hypothesis that ingestion of mixtures of amino acids based on EAAs (either with or without citrulline) will minimize changes in blood acidity and urea production as compared to the corresponding amount of the complete balanced mixture of EAAs and non-EAAs representing pig muscle. The specific aims will be tested in a chronically instrumented pig model prepared with indwelling catheters to enable sampling across the gut, liver, and muscle. The combination of arteriovenous sampling and stable isotope methodology will enable quantification of all endpoints. The results of this study should provide the basis for a new nutritional formulation to specifically support organ and tissue metabolism in sepsis.